<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <input type="text" id="a">
  <div>
    <p id="c"></p>
  </div>
  <span id="b"></span>
</body>
<script>
   o = {}
   Object.defineProperty(o, 'hello' , {
    set: function (newVal) {
      document.getElementById('a').value= newVal
      document.getElementById('b').innerHTML= newVal
    }
   })
   a.addEventListener('keyup',function(e){
    o.hello = e.target.value
   })
</script>
</html>